Non-contact vehicle wheel alignment measuring systems either use (1) structured light (i.e., light sources able to project a line of light onto the wheel) or (2) non-structured light. While structured light typically does not require the use of optical targets, the linear light projected onto the wheel can be a concern to operators of the vehicle alignment measuring system and their employers. Non-contact wheel alignment measuring systems that use non-structured light typically require optical targets, which are separate from the wheel and are mounted to the wheel.
In a non-structured light system, the separate optical targets are secured to vehicle wheels with wheel adaptors that clamp onto the wheel and position a mounting point for the wheel adaptors substantially coaxial with the axis of rotation of the wheel rim. A conventional optical target includes precisely engineered high-contrast optical elements such as circles, squares, or triangles. In one known system, the optical elements must be large enough to have relatively long straight or curved boundaries, and they must be separated far enough to prevent the individual optical elements from appearing to fuse into a single object when reduced edge sharpness causes two or more optical elements to bleed into the same pixel in the imaging system.